1. Field of the Invention
The present invention concerns a method to deposit oxynitride films (Mx(ON)y) containing at least one of metal, transition metal and transition metal alloy by reactive RF magnetron sputtering.
2. Description of the Related Art
Oxynitride films (Mx(ON)y) films are becoming increasing popular for their electrical, optical, wear resistant, and other functional properties. Mx(ON)y films are a relatively new class of materials with yet unexplored physical and chemical properties and a great potential for industrial applications. It is possible to continuously vary the values of, for example, refractive indexes, dielectric constants and transmittance of these films by varying the proportions between oxygen and nitrogen which are contained in the films.
For example, by depositing such an oxynitride film on a semiconductor surface, it is possible to use it as a surface passivation film, a surface-protection film, a gate-insulating film of field effect transistors, insulated-gate type static induction transistors, and an insulated-gate type semiconductor integrated circuit with these transistors. In addition, the film may serve as: a selective diffusion film employed in the planar semiconductor device manufacturing technique, a thin encapsulating film employed in a post-ion-implantation annealing technique, a masking film employed in a selective growth technique, a thin insulating film incorporated in active portions of an active device, and an insulating film for passive uses other than the use mentioned above. Furthermore, Mx(ON)y films are also use in thin film batteries as a solid state electrolyte which is disposed between an anode and a cathode. A suitable electrolyte comprises a lithium phosphorous oxynitride material which may be deposited on a substrate by radio frequency sputtering of a lithium phosphate target in a nitrogen gas.
Driven by improvements in deposition techniques, these thin film materials are commonly used in many vacuum coating applications. Reactive sputtering continues to emerge as one of the most economical methods for depositing compound thin films. With properly configured power delivery and process control measurements, high-rate, arc-free deposition of many oxides and nitrides becomes possible. As reactive sputtering methods becomes matured, interest in extending the technique beyond simple binary compounds has been growing. As material complexity increases, however, so do the challenges of process control as the inventors propose in this application.
The control of three sputtering gases in the sputtering process adds significant complexity and presents the issue of competing reactions. Since three sputtering gases can affect the state of the target surface and the plasma conditions.
Although the concept of reactive sputtering is quite simple, to employ it effectively to produce high quality insulating films at maximum rates is still a challenge. The nature of forming insulating layers in a DC sputter deposition is inherently disruptive to the process. In recent years the issue of arcing in reactive sputtering has been effectively managed by using one of several power delivery techniques. The most common power delivery techniques are applying pulsed-DC in a single magnetron system and applying low frequency AC power in a dual magnetron system. In both cases, a voltage reversal at the cathode is used to effectively eliminate charges built up on the target surface so as to avoid a breakdown event. Many modern power supplies also use arc detection and arc handing circuitry designed to quickly extinguish an arc if occurs.
The use of radio frequency (RF) to sputter materials was investigated in the 1960's. Davidse and Maiseel used RF sputtering to produce dielectric films from a dielectric target in 1966. In 1968, Hohenstein co-sputtered glass using RF and metals (Al, Cu, Ni) with DC, to form cermet resistor films. RF sputter deposition is not used extensively for commercial PVD for several reasons. The major reasons are it is not economic to use large RF power supplies due to high cost, introduction of high temperatures into insulating materials, and the high self-bias voltage associated with RF power.
The term “reactive sputtering” was introduced by Veszi in 1953. Reactive sputtering was used to deposit tantalum nitride for thin film resistors. However it wasn't until the mid-1970s that reactively sputter-deposited hard coatings on tools began to be developed, and they became commercially available in the early 1980s.
The sputtering process has almost no restrictions to the target materials, ranging from pure metals (using a DC-power supply) to semiconductors and isolators (using a RF-power supply or pulsed DC). Deposition is carried out in either non-reactive (inert gas only) or reactive (inert & reactive gas) discharges with single or multi-elemental targets. During the sputtering process, a magnetic field is used to trap secondary electrons close to the target. The electrons follow helical paths around the magnetic field lines undergoing more ionizing collisions with neutral gas near the target than would otherwise occur. This enhances the ionisation of the plasma near the target thereby leading to a higher sputtering rate. It also means that the plasma can be sustained at a lower pressure. The sputtered atoms are neutrally charged such that they are unaffected by the magnetic trap.
The method of gas-sequence control is basically used in epitaxy growth systems such as MOCVD and MOVPE for deposition of thin films.